All GRE Subject Test: Physics Resources
Example Question #1 : Fundamental Properties
A particle traveling through glass (index of refraction 1.33) emits Cherenkov radiation. Which of the following is a possible speed of the particle?
Cherenkov radiation is emitted by a particle traveling faster than the phase velocity of light in that medium. Because , the phase velocity of light in the glass is:
This is the minimum velocity of a particle to be emitting Cherenkov radiation in glass. This eliminates all answers except and . The latter is impossible because it is greater than the speed of light in a vacuum, therefore the answer is .
Example Question #2 : Fundamental Properties
A monochromatic beam of light travels through a material with a phase velocity of . What is the refractive index of the material?
The phase velocity of light through a medium with refractive index is given by:
Solving this for and substituting our given value of :